Rhesus monkeys fed experimental low-calorie diets didn’t live any
longer than their high-calorie brethren, a result that conflicts with a
2009 report of long-lived, extra-low-calorie monkeys.

That had been the first demonstration of extended lifespans in
primates, not just lab rodents, and raised hopes of the diet being a
dinner-plate fountain of youth. The new findings seem to challenge that
notion, though they’re far from conclusive.

More fundamentally, the findings pop the lid on a roiling scientific
back-and-forth over calorie restriction’s effects and mechanisms, a
matter of vigorous contention that’s belied by popular notions of the
diet as a simple, straightforward longevity hack.

“From the beginning, there have been people who were true believers
in the effects of calorie restriction in every single species,” said
Rafa de Cabo, a National Institute on Aging gerontologist and co-author
of the new study, published Aug. 29 in Nature. “Often attention
wasn’t paid to data showing that in some cases calorie restriction
wasn’t good, or didn’t produce the effects it should have.”

De Cabo’s experiment started in 1987, right around the time as
another, similar experiment at the University of Wisconsin. Both groups
wanted to know whether calorie restriction — cutting intake by up to 40
percent below what’s typically considered healthy — would have the same
health-protecting, life-prolonging effects in primates that it seemed to
have in lab animals.